The present invention generally relates to piston pumps and more particularly relates to piston pumps for use with hydraulic, slip-controlled brake systems.
A piston pump of the afore-described type has been taught, for example, by EP 0 631 050 B1. The state-of-the-art piston pump comprises a pressure valve and a suction valve the two of which are arranged separately from one another within a pump housing and are of different structural designs. In addition, the conventional pressure and suction valves are successively mounted in the pump housing and, in mounted condition, are permanently sealed therein in a way which precludes examination (without destroying portions of the pump assembly). However, even prior to assembly thereof it is difficult to carry out an optimum check of the valves because to do so requires simulation of the valve in its assembled condition.
It is especially the examples of embodiment of a conventional piston pump disclosed by FIGS. 11 through 19 of EP 0 631 050 that reveal a pressure valve designed as a ball valve, wherein the ball is biased against a seat formed as a radial bore, using an annular material. The said prior art valve involves some disadvantages to the effect that mounting of the annular material on the valve body of the pressure valve involves substantial efforts, and attachment thereof is not particularly stable. Moreover, the prior art arrangement does not prevent the valve body from twisting, so that the ball is likely to slip from the valve seat or to cause a change in the preloading force.
Moreover, EP 0 631 050 discloses an axially arranged suction valve prestressed by a helical spring held by a spring cage, with the helical spring and the holding element being located on the side of the suction valve facing the pressure chamber for which reason the brake fluid taken in has to be sucked through the spring coils, thereby substantially increasing the flow resistance.
The problem underlying the present invention, therefore, resides in avoiding the disadvantages involved with the prior state of art, in particular, to provide a piston pump wherein both the pressure valve and the suction valve prior to assembly thereof in the pump housing can be externally mounted and checked.
This problem, in the practice of the invention, is solved in that the pressure valve and the suction valve are formed within an individually handled (i.e. self contained) structural unit.
One advantage of the present invention resides in that in view of the inventive design of the pressure valve and of the suction valve in the form of an externally mountable and checkable valve cartridge unit, the number of components employed and the number of scrap valves are reduced thereby decreasing the manufacturing costs. Moreover, it is an advantage of the invention that the time needed for assembling the piston pump of the invention is substantially reduced thereby equally decreasing the manufacturing costs. In addition, the structural combination of pressure and suction valves will result both in space savings and in an optimum use of the space available for the valves within the pump housing. The structural combination of pressure and suction valves enables the valve body to be simply bored as there is no need to accommodate separate valves within the pump housing.
Preferably, the structural unit comprises a basic section and a section of sleeve-type configuration, it being especially the sleeve-type section that contains a substantially axial bore for guiding the piston. The bearing surface of the piston is thereby insensitive to deformation occurring by processing operations on the block. Moreover, the block is not required to be anodized to obtain wear-resistance of the bearing surface of the piston. In view of enhanced life requirements, wear resistance can, therefore, be improved only by a selection of material suitable for the structural unit.
A particularly cost-effective embodiment of the invention arises from the fact that the structural unit is secured within the housing of the piston pump by caulking or clinching.
Under structural aspects, for example, for space saving reasons, it is advantageous to form the pressure valve on the sleeve-type section and the suction valve on the base section, with the suction valve being arranged on the structural unit in axial and the pressure valve in radial relationship to the center axis.
According to a preferred embodiment of the invention, the structural unit is made of a plastic material, such as PEEK. It is not only for cost-saving reasons that this material is to be preferred but also because it permits to simultaneously mold valve elements. To that effect, the substantially axial bore, preferably, is conically shaped to enable the material core to be extracted. Preferably, the piston is also conically shaped. The two cones, in the working point of the pump, are adjusted to the work cycle of cylinder bore and piston to insure minimum play during operation of the pump.
Preferably, the structural unit is of a substantially constant diameter so that a simple bore within the pump housing will be adequate to accommodate and secure the structural unit therein.
According to another preferred embodiment of the invention, the base section is in the form of a separate unit. The extra costs involved with this bipartite configuration of the structural unit are more than compensated in view of the costs and manufacturing problems otherwise connected with the assembly of the suction valve within the structural unit due to the small diameter of the cylinder bore.
According to a particularly preferred form of embodiment of the present invention, the pressure valve comprises a closure body and a valve seat, with the valve closure body being prestressed by a preloading element against the valve seat thereof. To that effect, the preloading element and the valve closure body can be integrally formed thereby preventing the valve closure member from dropping during assembly and operation.
Advantageously, the preloading element is secured to the structural unit. Moreover, it is preferred to form the preloading element on a clip, preferably a tongue, adapted to be plugged onto the structural unit. The tongue can be made along with the clip, e.g. by punching. Moreover, the tongue insures that the contact pressure exerted on the valve closure body be always in the vertical direction to preclude wear on the valve seat.
Advantageously, the clip can be pushed onto the structural unit. With a design of the afore-described type, the preload on the valve closure body will not be affected.
According to a preferred form of embodiment of the invention, the clip comprises two sections extending in a direction substantially vertical with respect to one another, with the first section being pushed over the structural unit, and the second section being provided for preloading the valve closure body, thereby eliminating the need for special mounting means on the structural unit; during assembly, the part of the clip serving for preloading is not used, thereby insuring an optimum resilient effect. Preferably, the second section includes a tongue substantially bent by 180xc2x0, thereby enabling a maximum resilient length to be attained involving minimum space requirements.
According to a preferred embodiment of the invention, the valve seat is formed on a bore, with the valve closure body comprising a guiding section for guiding the valve closure body within the bore, resulting not only in a simplified assembly but also in reduced noise because the guiding section, during operation, will cause friction within the bore, thereby attenuating an oscillation of the valve closure body resulting in the generation of noise.
More advantageously, the preloading element is designed in the form of a leaf spring preferably extending in the longitudinal direction of the structural unit, with the leaf spring preferably being secured to the structural element externally of the bending zone thereof.
According to a further development of the invention, the suction valve of the piston pump comprises a valve closure body and a spring element for preloading the valve closure body against the valve seat thereof, with the spring element being located on the suction side of the suction valve, thereby substantially reducing the flow resistance during in-take of the brake fluid as the latter need no longer be sucked, past the spring element, for example by the coils of a helical spring.
Advantageously, the valve closure body comprises a sealing section and a guiding section. No additional holding element for the spring element is required if means for bearing one end of the spring element are formed on the outer side of the guiding section.
According to a preferred form of embodiment of the invention permitting a preliminary assembly of the suction valve, an element is provided on which is formed the valve seat for the suction valve and which, in addition, includes means for bearing the other end of the spring element.